This invention relates to facsimile systems comprising a transmitter, a receiver and a communications network such as telephone lines therebetween. The transmitter employs a scanning or reading element which reads the information content of an original document. The original document is moved relative to the reading means such that successive paths are scanned whereupon the output of the scanning element is fed to a device such as a photodetector which converts the variations in light intensity received by the scanning element due to variations in the reflectivity of the scanned document to electrical signals. These electrical signals then convey information concerning the radiation absorption, emission or reflection of the scanned document. The electrical information-bearing signals are then transmitted to a receiving unit over suitable means such as a telephone network where the receiving unit converts the electrical information-bearing signals from the transmitting unit to marks or images on a receiving copy medium so that the received copy is a reasonable facsimile of the original scanned document.
In one type of conventional facsimile system, the copy medium comprises a sheet of paper which is applied to the receiving drum with opposite edges of the paper abutting or overlapping so as to form an open loop having a discontinuous copy medium surface. In order to assure that the margin of the copy is appropriately located with respect to the edge of the sheet, angular synchronizing signals are utilized. These signals assure that the position of the document edge passes the reading head of the transmitter at the same time that the copy edge passes the writing head of the receiver, and this in turn assures the proper location of the copy margin with respect to the edge of the copy sheet. In other words, the copied matter is placed on the copy sheet in substantial conformance with its location on the document being copied.
U.S. Pat. No. 3,582,550 -- Latanzi is illustrative of the complexity which is involved in maintaining synchronization between transmitter and receiver drums in prior art systems. In this particular prior art system, a variable frequency generator drives the drum motor at the receiver in response to an error signal indicative of the relative positions and speeds of the transmitter and receiver drums. An elaborate clutch mechanism is shown in U.S. Pat. No. 3,569,628 -- Okleshen which is utilized in effecting synchronous phase operations between a transmitter and a receiver. These synchronizing arrangements add expense to a facsimile system as well as making it difficult to increase the rate of transmission.